An example of an application for an AC/DC converter is generating a DC voltage from three-phase AC power, the DC voltage then being modulated to provide controlled power to a variable speed AC motor, such as are commonly used in elevators and pump/compressor systems. A common AC/DC converter is formed of IGBTs. However, the IGBT devices are themselves very expensive, and the gate drive circuitry to control them is also expensive. In contrast, thyristors cost only one-tenth as much as IGBTs. The simplest and cheapest form of AC/DC converter is illustrated in FIG. 1. Therein, three-phase AC is fed through inductors 12 to a bridge 13 formed of diodes 14. A DC voltage is generated on positive and negative rails 15, 16, respectively, by a large capacitor or capacitor bank 17, and is applied to a load 18, such as a variable frequency, variable voltage DC/AC inverter of a known type. However, such a device has a very poor input current waveform, one phase of which is illustrated along with AC source voltage in FIG. 2. Another problem with diode bridges is that they do not handle returning power to the AC grid during regeneration, such as occurs when an elevator travels downwardly with a heavy load or travels upwardly with a light load.